Crystal polarization optical elements (prism polarizers, wave-plates) have inherent limitations (costly, limited sizes, bulky, sensitive to the angle of incidence, limited to low optical power, low operating temperature, and restricted to use in visible spectral range), which prevent usage in some applications. Some elements have complicated structures, for example, regular circular polarizes include at least a linear polarizer and a one-quarter wave-plate, which are highly costly and require extra-holding mounts.
The use of liquid crystal based optical elements provides benefits to overcome most of these drawbacks. For example, cholesteric liquid crystal optical elements provide good optical quality at large apertures, high contrast with angular insensitivity, high transmission for passed polarization, environmental stability, laser-damage resistance, and back-reflection protection. Chiral dopants may be used to modify the optical properties of a nematic phase. However, in some cases, fluidity of liquid crystals is a serious obstacle, which may be overcome by using vitrified liquid crystals, e.g., liquid crystal glasses. Liquid crystal glasses are promising materials for developing optical elements. In particular, cholesteric crystal glasses are potentially useful as large area non-absorbing polarizers, optical notch filters, optically-switchable notch filters and reflectors, and polarizing fluorescent films. Moreover, cholesteric glassy films may serve as a one-dimensional photonic band-gap for circularly polarized lasing.
Yet, not all liquid crystalline materials may be used to form uniformly aligned anisotropic glasses stable. To be useful, the targeted materials must possess elevated phase transition temperatures, stability against crystallization from the glassy state, and selective reflection across the visible to near-infrared region. For example, Chol-OOC—C5H10—C≡C—C≡C5H10—COO-Chol has been reported to have a cholesteric glass transition temperature of 80° C. Cholesterol-containing butadienes show cholesteric phase at elevated temperatures, such as one example having a glass transition temperature of 89° C. Cyclohexane-based cholesteric liquid crystal glasses demonstrate a glass transition temperature of −65° C. Benzene functionalized with hybrid chiral-nematic mesogens are room temperature cholesteric glasses with a glass transition temperature 73° C. Cholesteric cyclosiloxanes have a glass transition temperature of 62° C. Nonetheless, there remain at least two main problems: time stability and uniform alignment over large surface areas.
Platinum acetylides have shown promise as nonlinear optical materials due to a high linear transmission, broadband triplet state spectra, and efficient conversion to the triplet state (due to the heavy atom effect of the central platinum atom). However, the full potential of platinum acetylides has not yet been achieved.